1. Field of the Invention
The present invention relates to pulse code modulation (PCM) transmission and time division switching exchanges and, more particularly, to switching networks used in such exchanges.
2. Description of the Prior Art
PCM and TDM exchanges are well known. They make it possible to establish interconnections through time division trunk channels leading to a switching network, which is able to interconnect those channels.
In a known manner, if N is the number of trunks in an exchange as hereabove defined, and if P is the number of time division channels in each trunk, the Q bits, forming any message sample transmitted on one of the P channels of a trunk, are collected by a multiplexer. The multiplexer gets together P.Q bits from P time division channels to constitute a frame wherein, on the one hand, the Q bits of any sample and, on the other hand, the P samples from the P channels are serially transmitted to a unit called variously group equipment or supermultiplexer. Each supermultiplexer receives samples from R multiplexers in the form of distinct frames and provides at its output a higher rank multiplexing for those samples. The P.Q.R bits received from R multiplexers by a supermultiplexer are then transmitted via a switching network in the form of samples, each one grouping Q bits outgoing from one of the time channels.